Intrathoracic pacemaker

ABSTRACT

The present invention provides a fully intrathoracic artificial pacemaker. The pacemaker is of sufficiently compact size to allow for implantation of both the electrode and the power source within the chest cavity. In exemplary embodiments, a screw-type electrode is used for connection to heart tissue, and a relatively short lead is used to connect the electrode to a battery unit, which can comprise electronics for control of the pacemaker. An assembly for implanting the pacemaker, as well as methods of implanting the pacemaker, are disclosed. In embodiments, the device is designed as a fetal pacemaker.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage application ofPCT/US2010/037557, which relies on and claims the benefit of the filingdate of U.S. provisional patent application No. 61/184,329, filed 5 Jun.2009, the entire disclosures of both of which are hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the fields of medicine and medicaldevices. More specifically, the present invention relates to pacemakerssuitable for use in patients in need, including fetuses, and methods ofusing them to maintain an adequate heart rate in the patients.

2. Description of Related Art

Various devices for artificially providing an electrical impulse tocause or assist in the regular beating of a heart are known in the art.Such devices, commonly referred to as “cardiac pacemakers”, “artificialpacemakers”, or simply “pacemakers”, have evolved from the relativelyrudimentary electrical devices of the late 1950s and the 1960s to thehighly sophisticated, programmable devices that are now available.Although there is variation in design and implementation of pacemakers,in general, all of them have a common function: to provide an electricalstimulus to cardiac muscle tissue to cause controlled, rhythmiccontraction of the muscle tissue such that blood can be pumped throughthe heart, thus causing circulation of the blood throughout the body.

The design and use of cardiac pacemakers in adults are well established.In general, adult cardiac pacemakers consist of at least one conductiveconnector or electrode that attaches to heart tissue on one end and toan electrical lead on the other end. The lead is a relatively longconducting material that connects the electrode to a power supply,typically a lithium battery. Modern cardiac pacemakers includeelectronics to control the rate of pacing and to keep track of batterypower, among other things. Typically, an adult cardiac pacemaker has asize on the order of 10 cc and has one or more leads of about 40-60 cmin length. There are several methods of implanting a pacemaker. Thesemethods include those for epicardial pacing, which involves placing theelectrodes in contact with the outer wall of the ventricle (epicardium)to maintain satisfactory pacing. Epicardial pacing is the pacing methodof choice for babies because their veins are considered too small for atransvenous system. In contrast, transvenous cardiac pacing, also calledendocardial pacing, involves inserting a wire containing an electrodelead into a vein, preferably the subclavian vein, and passing it throughthe vein to either the right atrium or right ventricle. The procedure isfacilitated by fluoroscopy, which enables the physician or cardiologistto view the passage of the electrode lead. Permanent pacing with animplantable pacemaker involves connecting the opposite end of theelectrode lead and wire to the pacemaker generator (battery and controlunit). The pacing generator, or control/battery unit, is then surgicallyimplanted into the patient's chest (for transvenous systems) or theabdomen (for epicardial systems). In transvenous systems, the entireimplanted pacemaker thus includes a relatively long lead that runs fromthe heart, through a vein, and to a battery pack/control unit implantedin the patient's chest.

While design and use of adult pacemakers is a mature field, the samecannot be said for the design and use of fetal pacemakers. Rather, thefield of fetal pacemakers has yet to show a successful design andimplementation. To date, fetal pacemakers have been designed based onthe same concepts used for adult pacemakers. That is, designs for fetalpacemakers have employed an electrode and long lead connected to abattery unit. The electrode is contacted with the fetal heart tissue,and the battery unit is placed outside of the uterus. Such a design hasuniformly met with rapid failure due to movement of the fetus in theuterus, which causes dislodgement of the electrode from the fetal hearttissue.

SUMMARY OF THE INVENTION

The present inventors have recognized the need in the art for improvedfetal cardiac pacemakers, and have developed a solution for that need.In doing so, the inventors have also developed an improved cardiacpacemaker that is suitable for use in infants, children, and adults. Thepresent invention provides a cardiac pacemaker that can provideartificial electrical stimuli for sustained rhythmic beating of a heart.Where designed for use in a fetus, the pacemaker can be implanted inutero without significant harm to the developing fetus or the mother,and can function for extended periods of time without dislodging orotherwise failing. Where designed for infants, children, or adults, thepacemaker can be implanted quickly and under conditions that mightotherwise preclude successful implantation of a pacemaker. Like thefetal pacemaker, the pacemaker for infants, children, and adults can beimplanted without significant harm to the patient and can function forextended periods of time. In the disclosure that follows, particularattention is paid to embodiments relating to fetuses because the designof the pacemaker is particularly well suited and advantageous for use infetuses. However, it is to be understood that the concepts and detailsdiscussed are equally applicable to design and implementation of theinvention as it relates to other patients.

In a first aspect, the invention provides a fully implantable cardiacpacemaker. The pacemaker of the invention includes one or morerelatively short leads (also referred to herein as “wires”) that connecta source of power to electrodes (also referred to herein as “coils”)implanted in the heart muscle tissue. The power source can includeelectronics for control of the device, reporting of performance of thedevice, and other things. Unlike fetal pacemakers attempted in the past,the present pacemaker, where designed for use in a fetus, is fullyimplantable in the fetus, and thus avoids problems associated withmovement of the fetus within the uterus causing dislodgement of theelectrodes from the fetal heart. Providing a pacemaker that can be fullycontained within the body of a fetus overcomes a key obstacle in fetalpacemaker art.

The pacemaker device of the invention can be provided as part of adevice assembly for implantation of the device into a chest cavity, suchas a fetal chest cavity. In general, the device assembly comprises apacemaker device releasably attached to means for deploying thepacemaker device into a chest cavity. The device and insertion means arereleasably attached to each other by way of a wire, thread, string, orother similar structure, referred to herein as a “holder”. Typically,the device assembly comprises a distal region comprising the pacemakerdevice and a proximal region comprising the means for deploying thepacemaker device into the body of a patient. The pacemaker devicecomprises at its distal end at least one electrode (e.g., a screw-typeelectrode) for connecting the device to fetal heart tissue. Theelectrode is attached to a relatively short wire or lead that connectsthe electrode to a power source (e.g., a battery pack) located on theproximal end of the device. The power source also comprises a controller(e.g., a computer chip for controlling emission of electrical impulsesfrom the power source). Located proximal and releasably attached to thepacemaker device is a structure for deploying the pacemaker into thebody of a patient. For ease of reference, this structure is referred toherein as a “pusher”. The pusher is a relatively long rod-like elementthat has a diameter or width similar to or the same as the diameter orwidth of the pacemaker device, and which is sized to fit within thelumen defined by the inner surface of the trocar to be used inconjunction with the assembly. The pusher is of sufficient length toallow for inserting of the pacemaker device into the chest cavity of apatient, such as into the chest cavity of a fetus from a point outsideof the mother's body. In embodiments, the device assembly furthercomprises a housing, such as a tube (e.g., a trocar), having an exteriorsurface defining the outside of the assembly, and having an interiorsurface defining a lumen of the assembly housing in which the pacingdevice, pusher, and holder are located.

The present invention further provides a method for implanting a cardiacpacemaker into a patient, such as a fetus. In general, the methodcomprises inserting a device assembly through a trocar into the chestcavity of the patient to the point where the device assembly touchesheart tissue at a pre-selected location. Preferably, the trocar isinserted through the right side of the chest. After insertion of thetrocar, a device assembly according to the invention is inserted intothe interior space of the trocar through its proximal end. Using thepusher, the device assembly is passed longitudinally through the trocarto the point where the distal end of the pacemaker device (i.e., theelectrode) touches heart tissue. The electrode is then implanted in theheart tissue. Upon implantation, the heart is monitored for pacingprovided by the device. Upon confirmation of proper pacing, the deviceassembly is disassembled to release the pacemaker device from theremaining components of the device assembly, and to fully deploy thepacemaker device. In doing so, the pacemaker device is released from thepusher by disabling the holder. The holder and pusher are removed fromthe trocar and the trocar is removed from the body, leaving thepacemaker fully in the chest. If necessary or desired, the pacemakerdevice can be pushed out of the housing through physical movement of thepusher against the pacemaker device prior or during removal of thehousing from the chest. The power source/control unit of the device istypically designed to fit snugly against the inner wall of the trocar(or device housing, if present), but not so snugly as to precludesliding of the control unit through the trocar or housing duringdeployment. During retraction of the housing and after deployment of thepacemaker device, the power source/control unit is deployed in thethoracic cavity. If necessary or desired, the power source/control unitcan be pushed out of the housing and into the thoracic cavity throughphysical movement of the pusher against the power source/control unit.Process steps for implantation of the pacemaker can be followed usingany known technique, including fiber optic visualization, use ofnon-invasive radiation (e.g., real-time X-ray imaging, etc.),ultrasound, and the like.

Yet further, the present invention provides a method for artificiallypacing a heart, such as a fetal heart. According to the method, a fullyimplantable pacemaker according to the invention is implanted in thebody of a patient and the pacemaker is connected to heart tissue.Electrical impulses from the pacemaker cause artificial pacing of theheart. In embodiments, artificial pacing is achieved for at least oneweek. In preferred embodiments, artificial pacing is achieved for atleast two weeks. In some embodiments, artificial pacing is achieved forat least two months. The method is highly suitable for artificial pacingof fetal hearts for any reason, including complete heart block orhydrops fetalis. The method is achieved by a fully implanted, closedsystem entirely within the chest and implanted with a minimally invasivetechnique. These attributes make the invention highly advantageous forapplications involving fetuses.

The present invention includes pacemakers, methods of implantingpacemakers, and methods of using pacemakers in patients of all stages ofdevelopment and of all ages. That is, the concepts discussed herein aregenerally applicable to infants, children, and adults as well asfetuses. For example, a pacemaker device according to the invention canbe used for pacing in children and adults who might require urgentpacing or where venous access issues make implantation using standardpacing methods difficult. The pacing device (with pusher and holder) canbe implanted into an infant's, child's, or adult's chest via a housingor sheath introduced through the chest wall. For example, the pleural orpericardial cavities can be accessed via a needle through the chest wallusing well-known techniques, followed by placement of chest tubes orpigtail catheters as required. The tip of the housing or sheath can thenbe pushed up against the ventricular myocardium and the pacing deviceimplanted by advancing a device assembly to the tip of the housing orsheath (if necessary), then screwing the entire mechanism (device pluspusher) into the myocardium. When pacing is confirmed, the trocarhousing or sheath (as well as pusher) can be removed from the body andallow pacing of the heart for days to weeks (or longer if necessary ordesired). The invention thus provides an implantable pacing system thatallows for pacing in patients of all ages for an extended period oftime.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this disclosure, illustrate features of embodiments of theinvention, and together with the written description, serve to explaincertain principles of the invention. The accompanying drawings areprovided as examples of the present invention, and are not to beconstrued as limiting the scope or content of the invention.

FIG. 1 depicts an embodiment of the device assembly according to oneaspect of the invention, which is disposed within the central lumen of adevice assembly housing.

FIG. 2 depicts the embodiment of the device assembly according to FIG.1, showing additional detail regarding structural features of thepacemaker device, the pusher, and the holder.

FIG. 3 depicts an embodiment of the pacemaker device after implantationinto cardiac tissue and release from the device assembly.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

Reference will now be made in detail to various exemplary embodiments ofthe invention, examples of which are illustrated in the accompanyingdrawings. It is to be understood that the following detailed descriptionis provided to give the reader a better understanding of certain detailsand features of embodiments of the invention, and that the followingdescription is not to be understood as a limitation on the scope of theinvention.

One general aspect of the invention is a fully-implantable cardiacpacemaker. In the exemplary embodiment discussed now, the pacemakerrelates to a fetal pacemaker, with the understanding that the concepts,materials, and techniques are equally applicable to patients afterbirth. The pacemaker of this exemplary embodiment of the inventioncomprises at least one electrode for delivering an electric pulse tofetal cardiac tissue. The electrode can be fabricated from any suitablematerial or combination of materials that are electrically conductive,and is typically fabricated from one or more metals. Suitable materialsare known and widely used in the art. The electrode comprises aconnector that connects the electrode to fetal cardiac tissue on one endand to an electrically conductive lead (also referred to herein as awire) on the other end. While not limited in design, in exemplaryembodiments, the connector is provided in the shape of a coil or screw,which is capable of being embedded in fetal cardiac tissue through atwisting motion. Connectors that are suitable for use in the pacemakerdevice of the invention are known in the art, and any such connector maybe used.

The pacemaker further comprises one lead per electrode to connect theelectrode to a power source. The lead can be fabricated from anysuitable material or combination of materials that are electricallyconductive. Typically, the lead is fabricated from one or more metals,as known in the art. Typically, the lead further comprises an insulativematerial around the electrically conductive material(s) along the lengthof the lead to prevent transmission of electricity except through theends of the lead. Leads that are suitable for use in the pacemakerdevice of the invention are known in the art, and any such lead may beused. It is to be recognized that, in contrast to leads used in priorattempts to develop fetal cardiac pacemakers, the leads of the presentinvention are relatively short. That is, in contrast to prior attempts,rather than providing a relatively long lead (e.g., about 10 cm-15 cm inlength) that can span a distance from the fetal heart to the mother'sabdomen, the present device comprises a lead that is designed to spanonly the distance from the fetal heart to the fetal chest cavity (e.g.,about 2 cm-3 cm). Likewise, because a fully-intrathoracic pacemakerdesign for children and adults has not been devised before, the leadsfor pacemakers of those embodiments are likewise relatively short, suchas on the order of 5-10 mm.

The fetal pacemaker device further comprises a power source connected toone end of the lead(s). The power source provides electrical energy tothe electrode(s) and, where present, to a controller unit. The powersource is not limited in design or composition. However, in exemplaryembodiments, the power source is a battery or set of batteries inelectrical connection with each other. In embodiments, the power sourcecomprises a non-conducting covering. The size of the power source canvary depending on the life stage of the patient to be treated and thelength of time that pacing is desired. In general, the power source isdesigned to fit in the chest cavity or thorax of a fetus, child, oradult to be treated. While not limited in size, in general the powersource for fetal applications will be about 4 mm or less in diameter orwidth and 1 cm or less in length. For example, it can be from 1 mm to 4mm in diameter, such as 2 mm, 3 mm, or 4 mm. Likewise, the power sourcecan have a length of from 5 mm to 1 cm, such as 5 mm, 6 mm, 7 mm, 8 mm,9 mm, or 1 cm. Further, while not limited in size, in general, the powersource for child applications will be about 4-10 mm or less in diameteror width and 1-3 cm or less in length. Where desired, two or moreindividual batteries can be connected in series or in parallel toachieve the desired longevity, voltage, etc. Selection of theappropriate battery size, shape, and power will be made by thepractitioner after consideration of the amount of energy needed to pacethe fetal heart, the point in gestation of the fetus, the type of pacingand number of electrodes needed, the length of desired time forfunctionality, and other parameters of interest to the practitioner.Many of the same considerations are relevant to child and adultpacemakers, with the understanding that, with increasing size of thepatient, larger components may be used. Use of larger components canprovide additional longevity and power to the pacemaker device.

In preferred embodiments, the pacemaker device further comprises acontrol unit that controls the frequency and power of impulses sent tothe cardiac tissue. In general, the control unit comprises electronics.Control units for pacemakers are known in the art, and any suitabledesign can be used. In preferred embodiments, the control unit isprogrammed to alter the frequency of pacing when the power sourcereaches a pre-defined point of remaining stored energy. For example, acontroller can pace a fetal heart at 100 beats per minute. However, whenthe controller senses that the power source has only, for example,thirty-six hours of power life left, the controller slows the pacing to90 beats per second. This drop in heart rate can easily be detected bythe mother's obstetrician, and he can take an appropriate action (e.g.,induce labor, add an additional pacemaker). The control unit will have asize similar to the power source. In embodiments, the two are combinedas a single functional unit having a size according to the descriptionabove for the power source.

Another general aspect of the invention is a device assembly forimplantation of the pacemaker device into a chest cavity. In general,the device assembly comprises a pacemaker device for artificial pacingof a heart, a pusher for implanting the device into a patient, and aholder that holds the pacemaker device and pusher together. While notlimited in size, in general, the assembly is designed to fit within theinner diameter of a trocar that is suitable for use in surgery for thepatient of interest, or within a device housing. Thus, in general, thedevice assembly has a diameter or width of about 4 mm or less, such asfrom 4 mm to 1 mm, for example 4 mm, 3 mm, 2 mm, or 1 mm. Likewise, ingeneral, the device assembly has a length of about 10 cm-15 cm or morefor fetal applications. Thus, in embodiments, the device assembly has alength of 10 cm, 11, cm, 12 cm, 13 cm, 14 cm, or 15 cm. Longer lengths,such as 20 cm or 25 cm are also contemplated. In general, the deviceassembly has a diameter or width of about 4 mm to 10 mm or less, and alength of about 1 cm to 3 cm or more for child and adult applications.The practitioner may select any particular value falling within theseranges based on various considerations.

The assembly comprises a distal portion that is defined by a pacemakerdevice of the invention. Located proximal and releasably attached to thepacemaker device is a pusher. The pusher is a relatively long rod-likeelement for inserting the pacemaker device or the full device assemblyinto and through a housing from its proximal end outside of a patient'sbody to its distal end within the chest cavity of the patient. For fetalapplications the length is sufficient to extend from the proximal endoutside of the mother's body to its distal end within the fetal chestcavity.

The pusher may be fabricated out of any suitable material, and ispreferably made from a material that can be easily sterilized. Forexample, the pusher may be made from one or more plastic materials knownin the art as suitable for medical devices. The pusher is preferably,but need not necessarily be, made from a disposable material, such asknown for single-use in medical procedures.

The device assembly further comprises a holder. The holder functions toreleasably connect the pusher to the pacemaker. The holder can be anyelement that releasably connects the pusher to the pacemaker, and cantake any shape or size. In exemplary embodiments, the holder is astring, thin wire, or elastic band that sits in a two opposing groovescut along the walls of the pusher and power source of the pacemaker.When employed, the holder physically holds the pusher and pacemakertogether, such that they substantially form a single unit. When desired(e.g., when the pacemaker is implanted), the holder is cut, thusreleasing the pacemaker from the pusher.

The present invention uses the device assembly to provide a method forimplanting a cardiac pacemaker into a patient. The method permits fullimplantation of a pacemaker device into a patient, and provides asignificant improvement in artificial cardiac pacing, including in bothfetuses and in children or adults, particularly in situations where achild or adult is in need of urgent pacing and other pacing devicedesigns are incapable of being implanted quickly and effectively. Ingeneral, the method comprises inserting a trocar into the chest cavityof a patient. A device assembly according to the invention is theninserted into the interior space of the trocar to the point where theelectrode touches heart tissue. The electrode is then implanted in theheart tissue, the holder is cut, and the holder and pusher are removed.The device assembly housing is retracted from the chest cavity whileimplanting the power source and controller in the chest cavity. That is,after implantation of the electrode into the heart, the holder is cutand the housing is retracted while deploying the remaining portion ofthe pacemaker device into the chest cavity using, if necessary, thepusher to move the device out the distal end of the housing. Whereappropriate, the entry points for the trocar (e.g., mother's abdomen)are closed using standard techniques.

While various parameters and method steps may be altered to suitparticular purposes, the present disclosure provides both general andspecific guidance on practicing the invention. Those of skill in the artwill recognize variations and modifications to the specificallydisclosed embodiments that fall within the general teachings of thepresent document. For example, the present disclosure discussesbatteries as a power source for the pacemaker device. Those of skill inthe art will recognize that the shape of the battery is not critical, aslong as it does not interfere with deployment of the device within thepatient or with function of the device. Thus, the battery may take anycross-sectional geometry, such as round, square, or rectangular.

While embodiments relating to fetal pacing provide significantimprovements in treatment for such patients, other embodiments of theinvention relate to pacemakers for patients after birth, and suchembodiments provide significant improvements in treatment of suchpatients. In all embodiments, the device is a complete pacing systemthat can be implanted within the thorax without invasive surgery or theneed for transvenous access. For example, in urgent situations relatingto children and adults where ventricular pacing is necessary andvascular access cannot be easily achieved, the device can be insertedinto myocardium and allow for temporary pacing until a permanent pacingsystem can be implanted. Likewise, the device of the invention can beused to treat adults who present with significant bradycardia andrequire urgent pacing.

The device of the invention can also be used in adults who requireextended pacing and in whom standard transvenous or epicardial systemscannot be implanted. As is known in the art, emergency pacing cancurrently be performed by transcutaneous pacing (by use of large pads onthe chest), but this make ventilation extremely difficult and is notalways effective—it can generally only be used for a short period oftime. When more prolonged pacing is required (e.g., around 24 hours), atemporary pacing lead is placed (through the veins) and is pushed upagainst the ventricular myocardium. This technique, however, requiresvascular access and a degree of expertise in catheter manipulation toaccess the ventricle. In contrast to the current commonly availabletechnologies, the present invention allows pacing for weeks to months,if necessary or desired, with a pacemaker that can be implanted withoutvascular access and in an urgent fashion.

Reference will now be made to an exemplary pacemaker device and deviceassembly according to the invention. The exemplary embodiments discussedare depicted in the figures.

With reference to FIG. 1, a device assembly 100 is generally depictedwithin the interior of a housing 140. Device assembly 100 includespusher 120, pacemaker device 110, and holder 130. It is to be noted thatthe diameter of the device assembly is reduced in the figure solely forthe purpose of improved clarity of the drawing. As disclosed above, thedevice assembly will typically have a diameter or width only slightlysmaller than the inside diameter or width of the housing to be used.

With reference to FIG. 2, a more detailed view of device assembly 200 isshown. As in FIG. 1, FIG. 2 depicts device assembly 200 disposed withinthe inner lumen of housing 240. Device assembly 200 includes pusher 220,pacemaker 210, and holder 230. Holder 230 is disposed within groove 216,which comprises an open space on two diametrically opposed sides ofpusher 220 and pacemaker 210 that can accommodate holder 230. Pusher 220further comprises male connector 221 for rotationally locking pusher 220and pacemaker 210 such that neither is free to rotate, with respect tothe other, about a longitudinally central point. The figure depicts maleconnector 221 having a hexagonal cross-section. However, it is to benoted that any suitable non-circular cross sectional shape can be used,including, but not limited to, triangular, square, rectangular,pentagonal, octagonal, star-shaped, and elliptical.

As further shown in FIG. 2, device assembly 200 includes pacemakerdevice 210 with several structural elements. Pacemaker device 210comprises female connector 211 for rotationally locking pacemaker 210and pusher 220. It is to be recognized that the size of female connector211 is determined in conjunction with the size of male connector 221such that male connector 221 is not free to rotate within the spacedefined by female connector 221. In practice of an exemplary method forimplanting a pacing device according to the invention, rotationallocking of pusher 220 and pacemaker 210 allows transmission of twistingperformed on the pusher 220 by the practitioner outside the body (e.g.,outside a mother's abdomen) to pacemaker 210. In embodiments wherepacemaker 210 comprises a screw or coil-like connector (as shown inFIGS. 1-3), the twisting motion allows the practitioner to embed theconnector into the heart tissue.

Further with reference to FIG. 2, pacemaker 210 comprises structures forstoring and deploying an electrode. More specifically, pacemaker 210comprises recess 212 that can house lead 217, which is connected to coilretention mechanism 213 and the body of pacemaker 210. Holder 230 isdisposed within groove 216 on pusher 220 and pacemaker 210 and through aconduit (not depicted in FIG. 2; depicted as element 318 in FIG. 3) incoil retention mechanism 213. Placement of holder 230 through theconduit and along groove 216 permits holder 230 to retain pacemakerdevice 210 in connection with pusher 220. It is to be noted that, in thefigures, the pusher and pacemaker device are depicted as not being inphysical contact with each other. The depiction is for clarity purposesonly—the two elements are in physical contact with each other whenprovided as parts of an assembly. Further, while not shown withparticularity in the figures, recess 212 and coil retention mechanism213 are designed to have cross-sections that permit rotational lockingof the two. That is, similar to male connector 221 and female connector211, recess 212 and coil retention mechanism 213 have cross-sectionsthat interconnect and preclude rotational freedom between the two. Inthis way, a twisting motion imparted on pusher 220 outside a patient'sbody (e.g., outside a mother's abdomen) is translated to a twistingmotion through the body of pacemaker 210 and to electrode 214. Where acoil- or screw-type connector is used as part of electrode 214, thetwisting imparted outside the body results in implantation of theelectrode in cardiac tissue.

Pacemaker device 210 further comprises seat 215, which blocks coilretention mechanism 213 from fully entering recess 212 and providesadequate space for lead 217 during storage. In the exemplary embodiment,lead 217, which connects electrode (which in the embodiments depicted inthe figures is a coil or screw) 214 with the battery of pacemaker 210,can be bundled within recess 212. When holder 230 is cut and removedafter implantation of electrode 214 into cardiac tissue, electrode 214,coil retention mechanism 213, and lead 217 extend away from the body ofpacemaker 210.

Turning now to FIG. 3, an example of a partially-deployed pacemaker 310is depicted. The figure depicts pacemaker 310 after implantation ofelectrode 314 into cardiac tissue, but before final placement ofpacemaker 310 into the chest cavity. For the purpose of clarity, nohousing is depicted. As can be seen in the figure, the holder has beenremoved from groove 316 and conduit 318, and coil retention mechanism313 is no longer in contact with seat 315 and has exited recess 312.Lead 317 is partially unbundled as a result of movement of coilretention mechanism 313 away from recess 312. In the figure, lead 317 isdepicted as having a short length; this is for the purpose of clarity ofthe drawing only. It is to be noted that the length of lead 217 can beany suitable length that allows for placement of the body of pacemaker310 in the chest cavity of the patient while attaching electrode 314 tothe appropriate locus in the epicardium. Likewise, for the sake ofclarity, coil retention mechanism 313 is depicted as relatively long;however, the length can be any length that is appropriate and useful.Likewise, while the cross-section of coil retention mechanism 313 isdepicted as hexagonal, any suitable cross-sectional shape can be used.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the practice of the presentinvention and in construction of this device without departing from thescope or spirit of the invention. Other embodiments of the inventionwill be apparent to those skilled in the art from consideration of thespecification and practice of the invention. For example, the deviceassembly can include a device housing, sheath or other outer structurethat retains the pacemaker device, power/control unit(s), pusher, andholder. It is intended that the specification and examples be consideredas exemplary only, with a true scope and spirit of the invention beingindicated by the following claims.

The invention claimed is:
 1. An artificial cardiac pacemaker, saidpacemaker comprising, in electrical connection: a power source; acontrol unit; at least one lead that is in electrical communication withthe power source, wherein the lead is electrically conductive and is nolonger than 3 cm; and at least one electrode, each electrode being inelectrical connection with only one lead; said pacemaker furthercomprising: a recess structure having a non-circular cross-section andadapted to receive a complementary structure of a pusher to controlmovement about a longitudinal central point; wherein rotational lockingof the structure of the pusher with the recessed structure of thepacemaker allows transmission of a twisting motion performed on thepusher, and a mechanism for retaining the electrode(s) and lead(s) inclose proximity to the power source until the pacemaker is implanted andfunctioning; wherein the cardiac pacemaker is of sufficiently small sizeto be fully implanted in the chest cavity of a gestating fetus withoutcausing significant harm to the development and health of the fetus. 2.The pacemaker of claim 1, wherein the power source and control unit havea circular cross-section having a diameter of 4 mm or less.
 3. Thepacemaker of claim 1, wherein the pacemaker has a length of 1 cm orless.
 4. The pacemaker of claim 1, wherein the electrode has a spiral orcorkscrew shape.
 5. The pacemaker of claim 1, having a tubular shapewith a diameter of 4 mm or less and a length of 1 cm or less, having alead with a length of 3 cm or less, and having an electrode with aspiral or corkscrew shape.
 6. The pacemaker of claim 1, wherein thecross-section is one of triangular, square, rectangular, pentagonal,octagonal, star-shaped, or elliptical.